chandra kunchala wrote: >>Can you tell me, wat is the purpose of that no-argument constructor,

Without one the container cannot create an instance of the servlet. But, it's very rare for an explicit constructor to be coded into a servlet. Usually, the default constructor that the compiler provides is used.

>>Why it should required?

See above.

>>Why the servlet should be "public".

How would you expect the container to be able to create an instance otherwise?